Here is a sample of how to calculate the scrollTop after adding objects to the array.

The logic is:

Save the scrollTop and the scrollHeight before adding.

Add the items.

Set the scrollTop by calc the delta of the height (by adding new items) and scroll to this height + the old scrollTop.

Keep it in your mind that there is a "jump" between the adding items and the new scrollTop. I don't think that you can over it unless you do some fadeOut/fadeIn or scrollTo with transition to cover this "jump".